Cathode-ray tube apparatus



March 1958 w. F.' K. J. NIKLAS 2,827,585

CATHODE-RAY TUBE APPARATUS Filed Dec. 9, 1954 INVENTOR WILFRID FRANZ KONRAD JOHANN NIKLAS United States Patent i CATHODE-RAY TUBE APPARATUS Wilfrid Franz Konrad Johann Niklas, New York, N. Y., assignor, by mesne assignments, to North American Philips Company, Inc., New York, N. Y., a corporation of Delaware Application December 9, 1954, Serial No. 474,126

Claims priority, application Netherlands December 15, 1953 4 Claims. (Cl. 313-76) This invention relates to cathode-ray apparatus. for reproducing images on a screen, which apparatus comprise an ion trap.

As is well-known, it is desirable in cathode-ray tubes for reproducing images on a screen, for example for oscillography or television, in which use is made of electromagnetic deflection means, that the electron gun, i. e. the assembly of electrodes producing a beam of electrons, should be of a design such that a separation can be made between the paths of electrons and the paths of negative ions which are unavoidably present in such tubes. For this purpose several constructions have been suggested which have in common that the electrons and the ions are jointly deflected by an electrostatic field and that the electrons only are deflected back by a weak magnetic transverse field so as to be directed to the centre of the screen in the absence of a deflecting field. The negative ions which continue their path substantially linearly are collected. The electrostatic field by which the electrons and the negative ions are jointly deflected may be obtained in that the anode and/ or the electrode of the electron gun preceding the anode is or are bevelled on the adjacent sides with respect to the axis of symmetry. Furthermore, it has been suggested that the anode and the preceding electrode, on their adjacent sides, should be cut off straightly with respect to the axis of the tube and that theaxes of the said electrodes should be arranged in parallel, but not in line with one another. In all these cases an inclined or tilted electrostatic field ensues by which the ions and the electrons are jointly deflected.

It has been found that such systems suffer from a fault resulting from the inclined deflecting field. When the electrons are deflected back with the aid of a magnetic transverse field, it is found to be impossible for them to be brought again exactly into the axis of the anode. After the magnetic deflection, the electrons follow a line intersecting the axis at a small angle. It will be evident that the cathode ray can be directed to the centre of the screen located on the axis of the tube only if the anode occupies an inclined position with respect to the axis of the tube. Such an inclined, arrangement is very objectionable, since the completed electron gun is required to be fixed in position in the tube exactly at the correct angle.

In a known method the said difficulties may be avoided by utilising two oppositely directed transverse fields instead of a single magnetic transverse field. This requires two magnet constructions which occupy much space, thus limiting the space available for arranging a focusing device and the deflection coils.

The present invention provides means which permit of substantially avoiding the said disadvantages by the use of an electron gun of a particular construction.

A cathode-ray tube according to the invention for re- Patented Mar. 18, T1958 the tube. The electron gun comprises at least a cathode, a control electrode, a tubular anode and at least one electrode located between the anode and the control electrode, the axis of the electron gun coinciding with the axis of the tube. An ion trap action is produced by an electrostatic field between the anode andthe preceding electrode, which field is inclined with respect to the axis. The characterizing feature of the invention is that on the side adjacent the cathode, through a length at least equal to the, diameter of the aperture of the anode on that side, the cross-sections of the anode with surfaces at right angles to the axis are asymmetric figures with respect to each line parallel to the intersecting line of the plane of the cross-sections and the plane passing through the axis and at right angles to the plane in which the ions are deflected, whereby the length inside the anode of the intersecting line of the last mentioned plane and the plane ofthe cross-section is divided by the point of intersection with the axis into two pieces of different length, of which the larger one is located on that side to which the ions are deflected,

, The axis ofthe electron gun is to be understood to mean the perpendicular to the centre of the aperture of the control'electrodefor the passage of electrons.

In the simplest embodiment of a cathode-ray tube according to the invention the anode has the shape of a flattened cylinder.

Since the inclined electrostatic field extends in the anode at the most through a length equal to the diameter of the aperture of the anode on the side of the cathode, it is immaterial that the anode farther also has an asymmetric cross-section. However, for the sake of simplicity, the whole of the anode is frequently given a uniform cross-section. The anode and/ or the electrode preceding the anode is cut off on the side of the anode along a plane inclined to the axis of the tube. An inclined electrostatic lens thus ensues between the anode and the preceding electrode, for example an accelerating anode.

Instead of utilizing a flattened cylinder, the anode may beshaped in the form of an inclined cone.

In order that the invention may be readily carried effect, it will now be described by way of example, reference to the accompanying drawing, in which:

Fig. 1 is a longitudinal section of a cathode-ray according to the invention.

Fig. 2 is a cross-section of the anode of the cathoderay tube of Fig. 1.

Fig. 3 is a cross-section of the anode of an electron gun which is a variant of the electron gun used in a tube as shown in Fig. 1.

Figs. 4 and 5 are longitudinal sections of other variants used in a tube as shown in Fig.1.

in Fig. 1, the cathode-ray tube comprises a neck 1 and an adjoining widerconical portion 2. The conical portion contains a screen, 3, which is 'of luminescent material. Numeral 4 indicates a focusing coil and 5 and 6 indicate a set of deflection coils. The neck 1 of the tube contains the electron gun which in this case comprises a cathode 7, acontrol electrode 8, anaccelerating anode 9 and an anode 10. The longitudinal axis of the cathode-ray tube, which is at the same time the longitudinal axis of the electron gun, indicated by the line 11 11. Both the anode 10 and the accelerating anode 9 are cut ofi obliquely with respect to the axis 11711, flius resulting in an inclined electrostatic field between the electrodes 9 and 10. The beam of electrons and negative ions which is located in the axis in the electrode 9, is deflected by the inclined field as indicated by the dotted line. It is thus directed within the anode 10 to the wall at 12. Outside the cathode-ray tube there are arranged magnet poles 13 and 14 which exert a transverse force upon the beam directed to 12. This results into with tube - the anode is 13 mms.

enemas e p e in the electrons being deflected back to the axis 11-11. The ions are substantially not influenced, so that they are. collected by the wall at 12 and neutralised. If the anode would be circular-cylindrical in shape, the electrons could not be brought exactlyinto theaxis 11-11 by the single field provided by the magnet poles--13 and 14. They 'would then follow thefull line which is at an angle a with the axis. In the non-deflected position, the electrons would not strike the luminescence screen 3 at the point of intersection of this screen and the axis 1111,

' comprises two circular-cylindrical parts 16 and 17 which are notco-axial with the neck of the tube.

Fig. 4 shows a part of another electron gun which permits of obtaining a similar effect as with the flattened cylinders shown in Figs. 1, 2 and 3. The gun in this case comprises an inclined conical anode 18 of a shape such that the wall on the side of the impact point 19 of the ions is parallel to the axis 20 20. On the other side,

-' the wall of the anode moves away from this axis, so that it is ensured. asbefore, that the electrons leave the anode 18 exactly in the axis 20-20. The accelerating anode is indicated by 21.

In the embodiment of an electron gun as shown in Fig. 5, in which the accelerating anode is indicated by a 22, the'anode comprises a circular-cylindrical part 23 and an inclined conical part 24. The distance h is equal to the, diameter d of the aperture of the anode on the side of the cathode. As mentioned above, it may be larger,'but it must not be smaller. The figure clearly shows that in the conical portion 24 the distance p between the axis and one side of the anode, as measured along the intersecting line of a plane at right angles to the axis 25-25 and the plane of the beam ofions 26 (which is the plane of the drawing), is in each cross-section larger than the distance 4, measured along the same line, to the other side' of 'the anode'; in other words the wall a on the side to which the beam of ions is directe d moves away from the axis 2525 more rapidly than on the opposite side. a a

In order to illustrate a few specific embodiments of the invention some dimensions are given below for the system of Figs. 2 and 1 I i In Fig. 2, the length of the anode '10i s 4O mms., the

smallest distancenfrorn its axisto the left side in the cross-section is 6 mms. and to the right side the smallest distance is 3.3 mms. The deformation on the right side extends itself over the entire length of the anode. The

7 diameter of the aperture in the anode is 3.3 mms.

In Fig. 5 the'diameter d, which is equal to the length h, is 7.2 mms. The diameter of the cylindrical part of On the right side the length of this cylindricallpart is 19.5 mms. and on the left side 26 mms.

4 a neck portion having a longitudinal axis and an adjoining wider portion containing a screen luminescing upon electron bombardment, the center of said screen being aligned with the axis of the neck portion, an electron gun within said neck portion having a longitudinal axis coinciding with the axis of said neck portion and producing a combined beam of electrons and ions along the tube axis, said gun including a cathode, control electrode, additional electrode andanode arranged in that order, said anode and additional electrode producing an inclined electrostatic field causing the beam of electrons and ions to be bent away from the axis of the tube'toward one side of the anode, and means located substantially at the area of said bending and producing a single magnetic field to deflect back toward the axis only the electrons in said beam, whereby the ions are intercepted by the anode and whereby thedeflected-backelectron beam tends not to coincide with the tube -axis,'said anode having a shape whereby its wall portions on the said one side are further from the axis than its correspondingly-located wall portions on the opposite side, to thereby subject the deflectedback electron beam to an asymmetric field causing the beam to coincide thereafter substantially with thev'tube axis. 3 j

2. Apparatus including a cathode-ray tube comprising a neck portion having a longitudinal axis and an adjoining wider portion containing a screen luminescing upon electron bombardment, the center of said screen being aligned with the axis of the neck portion, an electron gun within said neck portion having a longitudinal axis coinciding with theaxis of said neck portion and producing a combined beam of electrons and ions along the tube axis, said gun including a cathode, control electrode, additional electrode and anode arranged in that order, said anode and additional electrode producing an inclined electrostatic field causing the beam of electrons and ions side of the anode, and means located substantially at the to be bent away from the axis of the tube toward one area of said bending and producing a single magnetic field to deflect back toward the axis only the electrons in said beam, whereby the ions are intercepted by the anode and whereby the deflected-back electron beam tends not to :coincide with the tube axis, said anode having an aperture 7 the size of said aperture being asymmetric relative to. the

tube axis, said asymmetry of the anode being such that its wall portions on the said one side are further from the axis than itscorrespondingly-located .wall portions on the opposite side,to thereby subject the deflected-back elecf tron beam to an asymmetric field causing the beam to coincide thereafter substantially with the'tube axis.

3. Apparatus as set forth in claiin 2 wherein the anode is a substantiallycylindrical member and the side thereof opposite to the said one side is substantially flat.

V 4; Apparatus as set forth in claimZ wherein the anode has an inclined, truncated, conical portion.

References Cited in the file of this patent UNITED STATES PATENTS 2,412,687

Klemperer Dec. 17,1946 2,460,609, 'Torsch Feb. '1, 1949 2,515,305 7 Kelar July 18, 1950 FOREIGN PATENTS 1,043,675 

